Method of forming a land grid array interposer

ABSTRACT

A land grid array (LGA) interposer structure, including an electrically insulating carrier plane, and at least one interposer mounted on a first surface of said carrier plane. The interposer possesses a hemi-toroidal configuration in transverse cross-section and is constituted of a dielectric elastomeric material. A plurality of electrically-conductive elements are arranged about the surface of the at least one hemi-toroidal interposer and extend radically inwardly and downwardly from an uppermost end thereof into electrical contact with at least one component located on an opposite side of the electrically insulating carrier plane. Provided is also a method of producing the land grid array interposer structure.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 11/365,366, filed Mar. 1, 2006, which claims thebenefit under 35 U.S.C. §119(e) of the filing date of U.S. ProvisionalPatent Application No. 60/715,261; filed Sep. 8, 2005; the disclosure ofwhich is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United States Government support underContract No. NBCH3039004, DARPA, awarded by the Defense, AdvancedResearch Projects Agency; whereby the United States Government hascertain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the provision of novel and unique LandGrid Array (LGA) interposers, which incorporate the structure ofmetal-on-elastomer hemi-torus and other geometrically configuredelectric contacts to facilitate an array of interconnections betweendiverse electrical components. The invention is further concerned with amethod of producing the inventive LGA interposers.

Land Grid Array (LGA) interposers, by way of example, provide an arrayof interconnections between a printed wiring board (PWB) and a chipmodule, such as a Multi-Chip Module (MCM), among other kinds ofelectrical or electronic devices. LGA interposers allow connections tobe made in a way which is reversible and do not require soldering as,for instance, in ball grid arrays and column grid arrays. Ball gridarrays are deemed to be somewhat unreliable on larger areas because thelateral thermal coefficients of expansion driven stresses that developexceed the ball grid array strength. Column grid arrays hold togetherdespite the stresses but are soldered solutions and, thus, do not allowfor field replaceability, which is important because it saves thecustomer or user significant costs in the maintenance and upgrading ofhigh-end computers for which LGAs are typically used.

2. Discussion of the Prior Art

The basic concept of utilizing LGA interposers to provide an array ofelectrical connections is well known in the technology. In thisconnection, reference may be made in particular to Hougham, et al., U.S.Patent Publication No. 2005/0106902 A1, which is commonly assigned tothe assignee of this application, and the disclosure of which isincorporated herein by reference in its entirety. This publicationdescribes LGA interposers which define structure consisting ofmetal-on-elastomer type electrical contacts, wherein a compliant contactconsists of an elastomeric material structural element partially coatedwith an electrically conductive material, preferably such as a metal, soas to form the intended electrical contact. However, there is nodisclosure nor suggestion of a compliant contact of an LGA interposertype providing multiple points of electrical contact for each gridpointin a configuration, such as is uniquely provided by the presentinvention.

Johnescu, et al., U.S. Patent Publication No. 2005/0124189 A1 disclosesan LGA-BGA (Land Grid Array-Ball Grid Array) connector housing andelectrical contacts which, however, do not in any manner disclose thenovel and inventive LGA interposer metal-on-elastomer structure asprovided for herein.

Similarly, DelPrete, et al., U.S. Pat. Nos. 6,790,057 B2 and 6,796,810B2; and Goodwin, et al., U.S. Pat. No. 6,293,810 B2, describe varioustypes of elastomeric electrical contact systems and devices which,however, do not at all disclose the features and concept of the presentinventive metal-on-elastomer LGA interposers and arrays pursuant to thepresent invention.

SUMMARY OF THE INVENTION

Metal-on-elastomer type LGA contacts, as described hereinabove, havebeen previously described in Hougham, et al. in which a compliantcontact consists of a structural element of a non-conductive elastomerthat is coated on a part of its surface with electrically conductivematerial, which resultingly forms the electrical connection. However, acompliant contact with multiple points of electrical contact for eachgridpoint is only disclosed by the present invention, wherein severalspecific geometries and variants are also described. Among these, ahemi-torus shaped element, such as being similar in shape to one-half ofa sliced donut in transverse cross-section) may be orientedconcentrically with respect to a via (or proximate thereto), the latterof which passes through an insulating carrier plane to the other sidethereof. Metal is deposited onto the external portions of thehemi-toroidal elastomer element in order to form a multiplicity ofelectrically conductive contacts.

There are two general instances of LGA interconnects made withhemi-toroidally shaped, or other kinds of structural contact elementsconstituted of elastomeric materials. In the first instance, holes orvias in an insulating carrier plane would first be filled with metal toform solid electrically conducting vias with a surrounding pad ordogbone pad. Onto these pads would be molded both top and bottomelastomeric LGA bodies possessing various shapes, for example,hemi-toroidal. Then in a final step, metal strips would be depositedfrom the via pad on each side up and over the apex or uppermost ridge ofthe elastomeric hemi-torus. As illustrated in the drawings, this wouldthen form a continuous electrical path from the highest point on the tophemi-torus shape to the lowest point on the bottom hemi-torus shape atseveral points for an individual I/O.

In the second instance, the insulating carrier is initially unmetallizedwith open holes on the desired grid pitch. Then, the top and bottomelastomeric bodies, for instance, hemi-toruses are molded andmetallization follows to form the electrically conducting path, asillustrated hereinbelow. In case that during molding, the open hole inthe insulator were inadvertently (or purposely) filled with elastomer,(e.g. siloxane), this can be removed in a controlled fashion by a coringor punch step to open a continuous pathway from the top surface to thebottom surface. Metallization can then be deposited on the exposedsurface, which is produced thereby in a desired pattern so as to formthe electrically conductive pathway.

In addition to the standard two-sided LGA interposer, i.e., on bothsides of an insulating carrier phone, a one-sided compliant contact isalso generally known in the art, and referred to as a “hybrid” LGA inwhich the contacts are soldered (ball-grid-array or BGA) to the circuitboard but form a compression connection with the module, as in Jobnescu,et al., this frequently being referred to as a “hybrid BGA/LGA” or a“hybrid LGA/BGA” interposer.

There are several types of hybrid BGA/LGA's commercially available;however, the present invention describes a new type of hybrid BGA/LGAcombining a metal-on-elastomer hemi-toroidally shaped top or uppercontact with a solderable (BGA) bottom or lower contact. This providessignificant advantages over existing technologies, and examples thereofare presented hereinbelow.

In one preferred embodiment, an insulating carrier plane with regularlyspaced through-holes is treated to create a metal pad on top to fill theholes with electrically conducting metal for a through via, and a bottomsurface, for example, by electroplating followed by photolithography.This produces a bottom surface with a pad for a BGA connecting to acircuit board. Then molded onto the top surface is a hemi-toroidal shapeof an elastomeric material, such as siloxane rubber. The hemi-torus islocated concentric to the metal via pad and surrounds it either fully orpartly so that the elastomeric inside edge of the hemi-torus eithertouches the metal via and pad or lies outside the boundary of the viaand pad. Then, metal is deposited to form a path of a continuouselectrical connection leading from the top of the elastomer hemi-torusto the pad, which connects to the electrically conducting via to thebottom side of the insulating carrier plane creating a continuousconductive pathway from top to bottom. The metal on the elastomer may bedistributed over the entire surface, or fabricated to consist of one ormore strips connecting the top of the hemi-torus to the via pad. In apreferred embodiment there can be employed three strips, separated by 60degrees from one another, although other quantities and spacing areshown herein. All of the strips start at the top of the torus, orslightly on the outside edge, and terminate on the pad in the center,this then providing multiple contact points, which is deemedelectrically desirable.

Entrapment of air in the center of the hemi-torus is of concern as itcould interfere with reliable seating of the electrical contact incompression. This potential concern can be mitigated by forming anopening or venting slit in the side of the torus during or aftermolding. Alternatively, any concern about entrapped air can be overcomeby making the metal strips which extend over the top of the hemi-torusthick enough to extend over the elastomer surface, so that the gapproduced between the uncoated area of the hemi-torus and the modulebottom when the metal is in contact with the module bottom providessufficient venting to allow a facile escape of air from the center ofthe hemi-torus upon actuation.

Another advantage to having multiple discontinuities in the hemi-torusshape resides in that each segment with its metal strip contact can moveindependently and better accommodate or compensate for non-uniformitiesin the mating surfaces.

The hemi-toroidal shape of the interposer can be molded from a compliant(rubbery) material onto each I/O position in an array, and metal stripsare fabricated on the top surface of this shape so that they willprovide multiple electrical pathways from a single chip module pad to asingle printed circuit board pad. When this compliant hemi-torus is thusmetalized, and preferably provided with discontinuities in the donutwall so that air would not be trapped preventing good contact, andprovided that the compliant button stays well adhered to the insulatingsubstrate or plane by virtue of anchoring holes, surface roughening, orsurface treatments or coatings, then a uniquely functioning LGA isreadily produced.

A structure pursuant to the invention possesses another advantage. Formodules or PCBs that have solder balls or other protruding conductivestructures, the LGA interposer array can be actuated into the module/PCBsandwich without the need for any separate alignment step or alignmentstructures. The ball will nest in the hemi-torus structure and centerand stabilize itself with respect to any lateral motion in the x-ydirections.

This provides another advantage which may sometimes be invoked, in thata module, which has had solder balls attached thereto, it in preparationfor an ordinary BGA solder reflow step could instead be redirected onthe assembly line for utilization in an LGA socket. Thus, a singleproduct number part (balled module) could be used in two separateapplications: 1) BGA soldering and 2) LGA socketing.

Such torus structures could be made by molding where the molds are madeby drilling or machining with a router-like bit. Alternatively, it couldbe made by chemically or photoetching of the mold material utilizing amask in the shape of a torus structure. The mask could be made byphotolithography directly on the mold die or could consist of a premadephysical mask (such as from molybdenum sheet metal) that was separatelyformed by photolithography and then applied to the mold die.

Another embodiment of this invention utilizes a hemi-torus that has beendivided into three or four sections, each of which have been metalizedto provide separate electrical paths, and whereby each section canrespond mechanically independently when contacted with a pad or solderball and can thus more reliably form a joint. Moreover, preferably asmall space between these sections is created to allow gas to escapefreely.

Pursuant to yet another embodiment, a number of the divided sections ofa single hemi-torus can be made taller to provide a lateral stop for thecase when a balled module is loaded preferably from one side thereof.

According to another embodiment, a wall shape of the sectionally-dividedhemi-torus curves back in and under to form a nest so that when a solderball is brought into contact therewith, it can be pressed down into thenest and snapped into place, or the shape could be curved simply to bestnest a solder ball held in place there against.

As described in another embodiment, the I/O consists of multiplehemi-toroidal conic sections or domes that are fabricated into a groupto service a single I/O. Each of these domes is metalized separately sothat when contact is made with a module pad, redundant electrical pathsare formed. The different contacts can also act independentlymechanically thus being better able to accommodate localnon-uniformities. A further modification would be to make a portion ofthe hemi-toroidal domes in such a group higher in the z-direction, thusproviding a mechanical stop for cases where a balled module is loaded inpart from one side, and thus able to constitute an alignment feature.

In the above embodiments, the structures and methods described can beapplied to either single sided compliant LGAs (aka hybrid LGA), i.e., onone side of the carrier plane only, or to double sided LGAs. Further,they can be applied to hybrid cases where the corresponding metal pad iseither directly in line with the center axis of the upper contact or maybe offset therefrom.

As shown in another embodiment, the compliant structures are in a linearform rather than based on a torus or groups of domes. From a linearcompliant bar, or alternatively a sectioned bar, multiple contact stripscan be formed for each I/O. Further, the multiple metal contact stripscould be located on different linear bars for a given I/O. Variousarrangements could include multiple metal strips on the same linearsection of compliant material, or on different adjacent linear bars in aline, or on different linear bars on either side of the central I/O via.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be made to the following detailed description ofpreferred embodiments of the invention, taken in conjunction with theaccompanying drawings; in which:

FIG. 1 illustrates generally diagrammatically, a metal-on-elastomer LGAinterposer array, shown in a transverse sectional view, pursuant to afirst embodiment of the invention;

FIG. 2A illustrates a modified embodiment of the metal-on-elastomer LGAinterposers, shown in a transverse enlarged sectional view;

FIG. 2B illustrates a perspective view of the LGA interposer array ofFIG. 2A;

FIG. 3 illustrates a perspective view of metal-on-elastomer LGAinterposers;

FIG. 4 illustrates a transverse enlarged cross-sectional view of the LGAinterposers of FIG. 3;

FIG. 5 illustrates a perspective view of a further embodiment of an LGAinterposer array;

FIG. 6 illustrates a transverse enlarged cross-sectional view of theinterposer array of FIG. 5;

FIG. 7 illustrates a perspective view of a further embodiment of ametal-on-elastomer LGA interposer array;

FIG. 8 illustrates a transverse enlarged cross-sectional view of the LGAinterposer array of FIG. 7;

FIG. 9 illustrates a perspective view of a still further embodiment of ametal-on-elastomer LGA interposer array;

FIG. 10 illustrates a perspective view of a further embodiment of an LGAinterposer array, which is similar to that illustrated in FIG. 7;

FIG. 11 illustrates a further embodiment in a perspective view of an LGAinterposer array showing a modification relative to that shown in FIG.10;

FIG. 12 illustrates a perspective representation of a further LGAinterposer array, which is somewhat similar to that of FIG. 10;

FIG. 13 illustrates a transverse enlarged cross-sectional view of theLGA interposer array of FIG. 12;

FIG. 14 illustrates a perspective view of a further embodiment of an LGAinterposer array;

FIG. 15 illustrates a transverse enlarged cross-sectional view of aportion of the LGA interposer array of FIG. 14;

FIG. 16 illustrates a transverse enlarged cross-sectional view of anembodiment which is somewhat similar to that of FIG. 14;

FIG. 17 illustrates a perspective view of a further embodiment of an LGAinterposer array;

FIG. 18 illustrates a transverse enlarged cross-sectional view of theLGA interposer array of FIG. 17;

FIG. 19 illustrates a perspective view of a modified embodiment of theLGA interposer array, relative to that shown in FIG. 17;

FIG. 20 illustrates a transverse enlarged cross-sectional view of aportion of the LGA interposer array of FIG. 19;

FIG. 21 illustrates a modified arrangement consisting of linear bars ofmetal-on-elastomer contacts shown in a perspective representation;

FIG. 22 illustrates a transverse enlarged cross-sectional view of aportion of the LGA interposer arrangement of FIG. 21; and

FIGS. 23-25 illustrate, respectively, alternative-processing conceptsfor providing the LGA interposer arrays in accordance with various ofthe embodiments described hereinabove.

DETAILED DESCRIPTION OF THE INVENTION

In the detailed description of the various embodiments, elements orcomponents, which are substantially similar or identical, are designatedwith the same reference numerals.

Referring to the embodiment of the metal-on-elastomer LGA interposerarray 10, as illustrated in FIG. 1 of the drawings, there are shown aplurality of the interposers 12 in the form of hemi-toroidally shapedelements or so called buttons (generally simulating the shape of atransversely sliced donut). Each of the LGA interposer buttons 12includes a plurality of circumferentially spaced flexible strip-likemetal elements 14 forming electrical contacts which reach from thetopmost surface 16 of each respective LGA button 12 to the via 18 whichextends through an insulating carrier pad 20 on which the LGA interposerbuttons are mounted, and down through the center of the LGA buttons soas to connect to a conductive pad 22 which surrounds through the throughvia on both sides of the carrier 20, and extends out along theinsulating carrier surface beneath the LGA so as to make electricalcontact at the other side or the lowermost end surface 24 of theinversely positioned lower LGA interposer buttons 26. Theelectrically-conductive flexible metal elements are primarily strips 14which extend from the uppermost end of the respective upper LGAinterposer buttons 12 inwardly into an essentially cup shaped portionextending to the hole or via 18 formed in the pad 22.

Consequently, by means of the pads 22, which are constituted ofelectrically conductive material or metal and which surround each of thethrough vias 18 formed in the dielectric material insulating carrierplane 20, these contact the ends of each of the metal strips 14, whichextend along the external elastomeric material surface of eachrespective LGA hemi-toroidally shaped interposer structure or button 12.Accordingly, electrical contact is made from the uppermost or top end ofeach respective LGA interposer button to the lowermost end 24 of each ofthe opposite sided LGA interposer buttons 26 at the opposite or lowerside of the insulating carrier plane 20.

With regard to the embodiment illustrated in FIG. 2A of the drawings,wherein the electrical elements 30 consisting of the strips positionedon the top surface 16 of the respective LGA interposer buttons 12 extendtowards the through via 18, in this instance, there is no electricallyconductive pad present as in FIG. 1, but rather the metallic orelectrically conductive strips 30 forming the flexible metal contactsextend from the uppermost end 16 of the upper LGA interposer buttons 12down through the via 18, the insulating carrier plane 20 to thelowermost ends or apices 24 of the lower inverted LGA buttons 26 on theopposite or bottom side of the structure 10.

In essence, in both embodiments, in FIGS. 1 and 2A, both the upper andlower LGA interposer buttons 12, 26 are mirror images and aresymmetrical relative to each other on opposite sides of the insulatingcarrier plane 20. With regard to FIG. 2B of the drawings, thisillustrates primarily a perspective representation of the array of theupper LGA interposer buttons 12 positioned on the insulating carrierplane 20.

Reverting to the embodiment of FIG. 3 of the drawings, in this instance,the flexible metal electrical contacts 34, which are positioned so as toextend from the upper ends 16 of each of the respective LGA interposerbuttons 12 through the via 18 in the insulating carrier plane 20, asalso represented in the cross-sectional view of FIG. 4, are designed tohave the electrical metal contacts forming a plurality of flexiblestrips 34, which extend each unitarily from the upper ends 16 to thelower ends 24 of the hemi-torus shaped buttons 12, 26 from above andbelow the insulating carrier plane 20 in a mirror-image arrangement.Hereby, the multiple, circumferentially spaced metal electrical contactstrips 34 extend from the uppermost point on one side of the insulatingplane to the lowermost point on the opposite side so as to formelectrical through-connections at both upper and lower ends and, ineffect, forming a reversible structure 10.

As shown in FIG. 5 of the drawings, in that instance, each of thehemi-toroidally shaped interposer buttons 12, 26, which are essentiallyidentical in construction with those shown in FIGS. 3 and 4 of thedrawings, have the metal contacts 40 formed so that they extend in acommon annular conductive sleeve structure 42 prior to continuingthrough the via 18, which is formed in the insulating carrier plane 20to the upper and lower ends 16, 26 of the LGA interposer buttons 24. InFIG. 6 of the drawings, these contacts 40 separate only into separatedstrip-like portions 42 at the extreme uppermost and lowermost ends ofthe LGA interposer buttons 12, 26 and then join together into theessentially annular structure 44 extending through the via 18 formed inthe insulating carrier plane 20.

Referring to the embodiment of FIGS. 7 and 8 of the drawings, theseillustrate essentially a structure 50 wherein LGA interposer buttons 12are arranged only on the upper surface 52 of the insulating carrierplane 20 in a manner similar to FIG. 1 of the drawings, and wherein theconductive strips 14 contact metallic or electrically-conductive pads 54extending respectively through each of the through vias 18 formed in theinsulating carrier plane 20. The lower surface of each metal pad 54, inturn, may have a solder ball 56 attached thereto in preparation for asubsequent joining, as is known in the technology.

As shown in the perspective representation of FIG. 9 of the drawings, inthat instance, the LGA interposer array structure 60, which is mountedon the insulating carrier plane 20, is similar to that shown in FIGS. 7and 8 of the drawings; however, a slit 62 is formed in the elastomericmaterial of each LGA interposer button 12, communicating with theinterior 64 thereof, and with the through via 18, which is formed in theinsulating carrier plane 20, so as to enable any gasses or pressuregenerated to vent from the interior thereof to the surroundings.

FIG. 10 of the drawings is also similar to the structure shown in FIG.7, however, in this instance, each elastomeric interposer button 12 hasa plurality of slits 62 or discontinuities formed in the annulartoroidally-shaped walls thereof, preferably intermediate respectiveflexible metal strips 14, which are located on the upper and inwarddownwardly extending surface of each elastomer buttons, so as to enableeach separate segment 68 to be able to resiliently or flexibly respondto changes or irregularities in the topography of elements contactingthe LGA interposer buttons 12. Also, each segment 68 between each ofrespective metal contact strips 14 may respond mechanically orindependently, so as not to only accommodate differences in topographywith a mating surface or differences in the shape of mating solderballs, but in cases where a solder ball will be pressed against thetoroidal contacts to produce an electrical connection. In effect, thiswill enable a mechanical or physical compensation for encountereddifferences in contact surfaces.

With regard to the embodiment of FIG. 11 of the drawings, which issomewhat similar to FIG. 10, in that instance, at least one or more ofthe segments 68, which are separated by the intermediate slits extendingthrough the LGA interposer buttons are different in height, so as tohave some of the segments 70 higher than others in a z- or verticaldirection relative to the plane of the insulating carrier plane 20. Inthis instance, two segments 68 of the four independent segments of eachrespective LGA interposer button 12 are shown to be lower in height thanthe other segments 70.

With regard to FIG. 12 of the drawings, in this instance, the arraystructure 74 of the hemi-toroidal LGA interposer buttons 76, which aremounted on the insulating carrier plane 20, the opposite or lower side78 of which has solder balls 80 connected to electrically-conductivepads 82 extending through the vias 18, has the centers 84 of therespective LGA interposer buttons 76, which have electrical strip-likecontacts 88 extending downwardly, as shown in FIG. 13, have a contouredinner wall configuration 90, which allows for nesting or a snap-fit witha solder ball (not shown), which may be brought into engagementtherewith. In this instance, FIG. 13 showing the cross-sectionalrepresentation of FIG. 12, illustrates the knob-shaped interior sidewallprofile 90 of the compliant interposer button with the separate metalcontact strips 88 extending upwardly along the interior of wall 90 tothe topmost end 92 of each respective LGA interposer button 76.

As illustrated in the embodiment of FIG. 14 of the drawings, in thisinstance, as also shown in cross-section in FIG. 15; multiple metalstrip contacts 88 extend from the top surfaces of the compliant LGAbutton structure 100, passing over the top surfaces 102 and extendingdown into the center part of the hole 104 provided in each interposerbutton 106, and meeting with a common pad-shaped metal conductor 108,which extends along the upper surface 110 of the insulating carrierplane 20 under the button in contact with strips 88 and outwardly untilreaching a via 112, which extends the metal pad downwardly through theinsulating carrier plane 20 and along the lower surface 114 thereof, soas to contact solder balls 116. This is illustrated in thecross-sectional representation of FIG. 15 of the drawings, which alsoshows a filled injection tube 120 extending through the insulatingcarrier plane 20 and a residue break off point 122, where an elastomerportion was separated from an injection port on a mold forming theentire LGA button structure. This embodiment, showing the filledinjection tube for the plastic material, is adapted for the method inwhich the injection molding of elastomeric material is implemented fromthe bottom side of the insulating carrier plane 20.

As shown in FIG. 16 of the drawings, which is essentially similar to theembodiment of FIG. 15, in that instance, this illustrates a fillerinjection tube, the mold (not shown) forming the LGA button structure isimplemented by injection molding from the top side of the mold, and aresidual mass of elastomer 132 can be ascertained extending from theside 134 of the elastic LGA button structure 100 from which it wasseparated at the injection port of a mold.

Also indicated in FIG. 16 are two types of anchoring holes in theinsulating carrier plane 20, wherein one hole 136 extends all the waythrough to the other side thereof, and wherein a blob 138 of residualexcess molding material penetrates slightly beyond the bottom surface ofthe insulating carrier plane 20. Another type of anchoring hole orcavity 140 does not extend fully through the insulating carrier plane20, but is formed as a depression in the top surface of the latter, soas to mechanically anchor the elastomeric material of each LGAinterposer button to the structure or plane 20.

Reverting to the embodiment of FIGS. 17 and 18 of the drawings, theseshow another aspect of providing an LGA interposer array 150 on aninsulating carrier plane 20, wherein a multiple of LGA interposerbuttons 152 of essentially conical configurations and their electricalmetallic strip contacts 154, which extend over the topmost ends 156thereof, service a common I/O electrical contact 158 in the form of apad on the upper surface of plane 20. In this instance, the structureincorporates an electrically conductive via 160 extending through theinsulating carrier plane 20, shown in a center of a group of four LGAinterposer buttons 102, as a common meeting point of the metal contactstrips 154 on pad 158, which extend from respectively one each of thetop of each LGA button down the side thereof and into the via metallurgyof the structure, towards the bottom of plane 20, as shown incross-section in FIG. 18 of the drawings.

Reverting to the embodiment of FIGS. 19 and 20 of the drawings, which isquite similar to the embodiment of FIGS. 17 and 18, in that instance,the primary distinction resides in that at least one or two of the LGAinterposer buttons 152 of a respective group thereof has or have aheight which differs from the remaining interposer buttons of thatgroup. For example, two or more buttons 152 of each group may be tallerthan the remaining buttons 164 of that group (of four buttons) in orderto essentially create a lateral stop mechanism for a side loading of amodule, through such groupings of LGA interposer buttons in respectivearrays. In essence, the different heights in the LGA interposer buttongroups enable a module with an associated solder ball to be brought intocontact and aligned by means of lateral insertion, rather than onlyvertical insertion, wherein the higher LGA interposer buttons providestops for the solder balls in order to register with the essentiallyhemi-toroidally shaped elastomeric contacts.

Reverting to the embodiment of FIGS. 21 and 22 of the drawings, in thisinstance, there is provided an LGA interposer array 170 arranged on aninsulating carrier plane 20, wherein multiple points of contact for eachI/O are provided by means of linear bars of elastomeric LGA interposers172. This provides a compliant structure on which a plurality of spacedmetallic electrical contact strip elements 174 may be positioned so asto extend from the top 176 of each respective interposer bar 172 bothabove and below the insulating carrier plane 20, as shown in FIG. 22,into electrically sleeve-like conductive vias 178 formed extendingthrough the insulating carrier plane 20 in contact with respective metalstrip contacts 180 above and below the insulating carrier plane 20. Inthat instance, the metal contact strips 180 may be formed with differentshapes, such as one typical contact joining from two separate ships 182into a single common strip 184 near the top, as clearly illustrated inFIG. 21, or joining further down near the via extending through thecarrier plane to the other side. Furthermore, three or more contactpoints for each I/O may be provided and different types of contactelements may be utilized along the bar whereby some types may be moresuitable for conduction of signals and others for high amperage powerfeeds.

As illustrated in FIGS. 23-25, there are shown alternate process flowsfor a balled module, wherein a balled module zoo, as shown in FIG. 23,can be directed either towards a solder reflow line for normal BGAconnection to a PWB, as illustrated in FIG. 24, or alternatively, to anLGA interposer assembly 210 where it is assembled by means of ahemi-toroidal LGA and PWB (wiring board) under pressure to make a fieldreplaceable unit, as shown in FIG. 25 of the drawings.

With regard to the configurations of the LGA interposer buttons, thesemay be of elastic structural members, which are conical, dome-shapedconic sections or other positive release shapes, such as roughlycylindrical or hemispherical, hemi-toroids, and wherein the metalcoating forming the electrically conductive contact members or stripsterminate at the apices of each of the multiple buttons.

Moreover, the elastomeric material, which is utilized for each of theLGA interposer buttons or for the linear shaped elastic structuralmember (as shown in FIGS. 21 and 22) may be constituted of any suitablemolded polymer from any rubber-like moldable composition, which, forexample, among others, may consist of silicon rubber, also known assiloxane or PDMS, polyurethane, polybutadiene and its copolymers,polystyrene and its copolymers, acrylonitrile and its copolymers andepoxides and its copolymers.

The connectors of the inventive LGA structure may be injection molded ortransfer molded onto an insulating carrier plane 20, and may serve thepurpose of mechanically anchoring the contact to the insulating carrierplane and in instances can provide a conduit for the electricalconnections which pass from the top surface of the connector to thebottom surface thereof.

In addition to connecting chip modules to printed circuit boards, thearrays of the LGA interposer buttons or linear structure may be employedfor chip-to-chip connection in chip stacking or for board to boardconnections, the contacts may be of any shape and produced by injectingthe elastomer in the same side as where the elastomer contact will beanchored to the insulating carrier by a hole or holes or vias, whichextend through the insulating carrier or by any cavity edge formed intothe surface of the insulating carrier.

In essence, the molding of the elastomeric material component orcomponents, such as the hemi-toroidal interposer or interposers may beimplemented in that the elastomeric polymer material is ejected from thesame side at which the interposer will be positioned on the insulatingcarrier plane, and will be anchored to the insulating carrier plane bymeans of a hole or holes, as illustrated in the drawings, which eitherextend completely through to the opposite side of the insulating carrierplane, or through the intermediary of a cavity which is etched or formedinto the surface of the insulating carrier plane, which does not extendall the way through the thickness thereof, and wherein any cavity mayhave flared undercut sidewalls from maximum anchoring ability or bysimple surface roughening of the insulating carrier plane. This isclearly illustrated in the embodiments represented in FIGS. 15 and 16 ofthe drawings.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the scope and spirit ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of forming a land grid array (LGA) interposer structure,comprising: providing an electrically insulating carrier pad; mountingat least one interposer on a first surface of said carrier pad, saidinterposer selectively having a hemi-toroidal, conical, dome-shapedconic section, generally cylindrical or hemi-spherical configuration intransverse cross-section and being constituted of a dielectricelastomeric material; providing a plurality of electrically-conductiveelements for arrangement about the surface of said at least onehemi-toroidal interposer and extending radially inwardly and downwardlyfrom an uppermost end thereof into electrical contact with at least onecomponent located on an opposite side of said electrically insulatingcarrier pad, said at least one component comprising at least onehemi-toroidal interposer and at least one further hemi-toroidalinterposer mounted on said opposite side of said carrier pad and whichis identical to and in an inverted relationship with saidfirst-mentioned at least one hemi-toroidal interposer; and extending anelectrically-conductive solder pad member through at least one via andhaving portions extending in surface contact with upper and lowersurfaces of said insulating carrier pad, said at least one hemi-toroidalinterposer and said at least one inverted hemi-toroidal interposer beingat least partially located on, respectively, the upper and lower surfaceof said insulating carrier pad, whereby the electrically-conductiveelements are in contact with the respective surfaces on said solder pad.2. A method of forming a land grid array (LGA) interposer structure asclaimed in claim 1 , further including: forming said at least onethrough-extending via in said electrically-insulating carrier pad, saidelectrically-conductive elements comprising metallic strips formingelectrical connections between said first-mentioned at least onehemi-toroidal interposer and said further at least one invertedhemi-toroidal interposer.
 3. A method of fowling a land grid array (LGA)interposer structure as claimed in claim 2, further comprising:extending each said metallic strips to provide electrically-conductivepaths between the uppermost end of said at least one hemi-toroidalinterposer on the first surface of said carrier pad and the lowermostend of the at least one inverted hemi-toroidal interposer on theopposite side of said carrier pad.
 4. A method of forming a land gridarray (LGA) interposer structure as claimed in claim 3, furthercomprising: joining said metallic strips intermediate the uppermost andlowermost ends thereof to form an electrically-conductive cylindricalportion extending through the at least one via in said insulatingcarrier pad.
 5. A method of forming a land grid array (LGA) interposerstructure as claimed in claim 1, wherein said electrically-conductiveelements comprise metallic strips extending into contact with the solderpad portion on the upper surface of said solder pad, and the componentson the opposite side of said insulating carrier pad with the solder padportion on the upper surface of said solder pad, and the components onthe opposite side of said insulating carrier pad being inelectrically-conductive contact with the solder pad portion on the lowersurface of said insulating pad portion.
 6. A method of forming a landgrid array (LGA) interposer structure as claimed in claim 1, whereinsaid at least one interposer is constituted of a dielectric elastomericmaterial.
 7. A method of forming a land grid array (LGA) interposerstructure as claimed in claim 6, wherein said elastomeric materialcomprises a moldable polymer having rubber-like resilientcharacteristics.
 8. A method of forming a land grid array (LGA)interposer structure as claimed in claim 7, wherein said polymer isselected from the group of materials consisting of silicon rubber,siloxane, PDMS, polyurethane, polybutadiene and copolymers thereof,polystyrene and copolymers thereof, acrylonitrile and copolymersthereof, and epoxides and copolymers thereof.